Why Is That There? EDTA in shampoo

I’m gonna try out a new feature on this blog, called Why Is That There?  In it, we’ll explore various strange and sometimes baffling ingredients in common products, and find out just why the ingredient is there.  After all, manufacturers don’t add ingredients for no reason.  It’s just not a reason that we, the general public, probably know.

We’ll start out with the one that first really piqued my interest in weird product ingredients: EDTA.  I’m a cheapskate, so I use cheap shampoo: I wash my hair with Suave.  And one of the ingredients is tetrasodium EDTA.  It’s in nearly every shampoo, and a lot of body washes and hand soaps and laundry detergents as well.  Sometimes its close cousin disodium EDTA is there instead, or the label might just say “EDTA”.

So what the heck is it?

EDTA stands for ethylenediaminetetraacetic acid.  Try saying that five times fast.  Or even once, for that matter.  It’s in a special class of chemicals called chelators.  A chelator (pronounced “key-late-or”) is a chemical that bonds in a particular way to metal ions.  (The word comes from the Greek “chele”, which means “claw”.  The idea is that the molecule is claw-like in the way it bonds to a metal ion.)  Chelators bond extremely well to particular metal ions, so well in fact that you can use them medicinally to treat lead and mercury poisoning.  However, they tend not to be especially fussy about *which* metal ions they go for, so chelation therapy should not be considered lightly — there is a very real risk of chelating out all the calcium ions in your blood, which would not only stop your heart, it would make it impossible to revive you with the zappy paddles since it would rob your heart muscle fibers of the calcium ions that they need to contract.  That’s right: calcium is for way more than just strong bones.  You need it to make your nerves and muscles work.  That’s why your body will happily strip it from the bones if you’re running low; that’s far less critical.

Misused EDTA therapy has killed patients; it’s that dangerous.  So why are we slathering this stuff on our heads?  Are the guys at SC Johnson and Proctor and Gamble et all out to kill us?

Of course not.  Turns out, EDTA is completely incapable of penetrating the skin, so it’s totally safe to slather it on our bodies.  And there’s something really helpful it can do.  It’s a chelating agent, and very good at stripping calcium.  And guess what the most common culprit in hard water is?  That’s right: calcium.  Detergents don’t work well in hard water, so unless your water is really, really, ridiculously soft, you may find the shampoo rather disappointing.  So years ago, shampoo manufacturers started including EDTA to soften the water as you go.  And it works great!  The calcium is stripped out of the water you’re using to wash your hair, the shampoo works much better, and you come away happy and smelling fresh.  😉



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